package com.alibaba.cloud.utils;

import java.net.Inet4Address;
import java.net.UnknownHostException;
import java.util.Random;


/**
 * The Class SnowFlakeUtil.
 *
 * @ClassName: SnowFlakeUtil
 * @Description:雪花算法工具类(原生wiki)
 * @author: zhb1316783262@163.com
 * @date: 2020年4月6日下午8:17:24
 */
public class SnowFlakeUtil {

    /** The Constant SIGN_LEN. */
    private static final int SIGN_LEN = 1;
    
    /**  时间部分所占长度. */
    private static final int TIME_LEN = 41;
    
    /**  数据中心id所占长度. */
    private static final int DATA_LEN = 5;
    
    /**  机器id所占长度. */
    private static final int WORK_LEN = 5;
    
    /**  毫秒内序列所占长度. */
    private static final int SEQ_LEN = 12;

    /**  定义起始时间 2015-01-01 00:00:00. */
    private static final long START_TIME = 1420041600000L;
    
    /**  上次生成ID的时间截. */
    private static long LAST_TIME_STAMP = -1L;
    
    /**  时间部分向左移动的位数 22. */
    private static final int TIME_LEFT_BIT = 64 - SIGN_LEN - TIME_LEN;

    /**  自动获取数据中心id（可以手动定义 0-31之间的数）. */
    private static final long DATA_ID = getDataId();
    
    /**  自动机器id（可以手动定义 0-31之间的数）. */
    private static final long WORK_ID = getWorkId();
    
    /**  数据中心id最大值 31. */
    private static final int DATA_MAX_NUM = ~(-1 << DATA_LEN);
    
    /**  机器id最大值 31. */
    private static final int WORK_MAX_NUM = ~(-1 << WORK_LEN);
    
    /**  随机获取数据中心id的参数 32. */
    private static final int DATA_RANDOM = DATA_MAX_NUM + 1;
    
    /**  随机获取机器id的参数 32. */
    private static final int WORK_RANDOM = WORK_MAX_NUM + 1;
    
    /**  数据中心id左移位数 17. */
    private static final int DATA_LEFT_BIT = TIME_LEFT_BIT - DATA_LEN;
    
    /**  机器id左移位数 12. */
    private static final int WORK_LEFT_BIT = DATA_LEFT_BIT - WORK_LEN;

    /** ------------------------------------------------------------------------- SIGN_LEN |   TIME_LEN     |    DATA_LEN  |    WORK_LEN | SEQ_LEN    |      0    |      41        |      5(31)   |    5(31)    | 12(4095)   | -------------------------------------------------------------------------. */
    /** 上一次的毫秒内序列值 */
    private static long LAST_SEQ = 0L;
    
    /**  毫秒内序列的最大值 4095. */
    private static final long SEQ_MAX_NUM = ~(-1 << SEQ_LEN);

    /**
     * Generate id.
     *
     * @return the long
     */
    public synchronized static long generateId() {
        long now = System.currentTimeMillis();

        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if (now < LAST_TIME_STAMP) {
            throw new RuntimeException(String.format("系统时间错误！ %d 毫秒内拒绝生成雪花ID！", START_TIME - now));
        }

        if (now == LAST_TIME_STAMP) {
            LAST_SEQ = (LAST_SEQ + 1) & SEQ_MAX_NUM;
            if (LAST_SEQ == 0) {
                now = nextMillis(LAST_TIME_STAMP);
            }
        } else {
            LAST_SEQ = 0;
        }

        // 上次生成ID的时间截
        LAST_TIME_STAMP = now;

        return ((now - START_TIME) << TIME_LEFT_BIT) | (DATA_ID << DATA_LEFT_BIT) | (WORK_ID << WORK_LEFT_BIT)
                | LAST_SEQ;
    }

    /**
     * 获取下一不同毫秒的时间戳，不能与最后的时间戳一样.
     *
     * @param lastMillis the last millis
     * @return the long
     */
    public static long nextMillis(long lastMillis) {
        long now = System.currentTimeMillis();
        while (now <= lastMillis) {
            now = System.currentTimeMillis();
        }
        return now;
    }

    /**
     * 获取字符串s的字节数组，然后将数组的元素相加，对（max+1）取余.
     *
     * @param s the s
     * @param max the max
     * @return the host id
     */
    private static int getHostId(String s, int max) {
        byte[] bytes = s.getBytes();
        int sums = 0;
        for (int b : bytes) {
            sums += b;
        }
        return sums % (max + 1);
    }

    /**
     * 根据 host address 取余，发生异常就获取 0到31之间的随机数.
     *
     * @return the work id
     */
    public static int getWorkId() {
        try {
            return getHostId(Inet4Address.getLocalHost().getHostAddress(), WORK_MAX_NUM);
        } catch (UnknownHostException e) {
            return new Random().nextInt(WORK_RANDOM);
        }
    }

    /**
     * 根据 host name 取余，发生异常就获取 0到31之间的随机数.
     *
     * @return the data id
     */
    public static int getDataId() {
        try {
            return getHostId(Inet4Address.getLocalHost().getHostName(), DATA_MAX_NUM);
        } catch (UnknownHostException e) {
            return new Random().nextInt(DATA_RANDOM);
        }
    }
}
